The present invention is an improvement to U.S. Pat. No. 4,514,734 issued to the assignee of the present application. The antenna system disclosed in the patent provides a scanning antenna array system having low sidelobes in both the electronic and mechanical scanning modes. Further, the antenna array system set forth therein exhibited low mutual electromagnetic coupling between individual antenna elements. That system further exhibits smooth antenna in-array element patterns, improved power transfer characteristics when electronically scanned, and relatively high and uniform gain over a finite bandwidth.
Yet another advantage of the prior art system was its suitability for aircraft use and scannability over a total angle of about 90.degree. with excellent gain uniformity throughout the scanning range. The design was adapted to low profile configurations for installation in leading and trailing edge airfoils having reasonably large cross sections.
In particular, the structure of the patented antenna comprised vertically stacked arrays, each having a plurality of mutually parallel-spaced directors physically mounted to the internal surface of the wings. As the wings of high-performance aircraft become thinner, with the result that less room is available in the leading edge, such a physical assembly of antenna components becomes impossible. Accordingly, a new type of Yagi antenna array assembly that is small with respect to wavelength is necessary. The challenge then becomes designing the antenna to be efficient and still practical for such aircraft.